In the conventional power transmission belt, such as an automotive fan belt, the looped belt is provided with longitudinally extending tensile cords. Such belts are conventionally formed of resilient material, such as rubber, and the tensile cords are formed of relatively low stretch, high strength materials.
One known material for use in such tensile cords is polyester synthetic resin. An excellent example of such a synthetic resin advantageously adapted for such use is the polyester filament yarn sold by Celanese Corporation under the trademark Fortrel.RTM.. One form of such Fortrel.RTM. polyester resin manufactured and sold by Celanese Corporation is identified as the Type 111 polyester and has been utilized as tensile cords in such power transmission belts, as discussed above.
The use of polyester tensile cords in power transmission belts is disclosed in U.S. Pat. No. 4,522,614 of Hiroshi Matsuoka et al. As disclosed in that patent, an automatic tension-maintaining power transmission belt is formed by embedding polyester fiber cord having high relative viscosity and subjected to hot stretching prior to the embedment thereof in the rubber of the belt.